Find the part of the sentence that contains an error: Were he to have responded promptly (1)/ the crisis could have been (2)/ averted far earlier than it ultimately was (3)/ saving valuable diplomatic capital. (4)

Correct — A. The main clause, could have been averted, looks back at a past event that did not happen: a past unreal condition.

Its standard inverted form is Had + subject + past participle: 'Had he responded promptly...'

Segment (1) uses Were he to have responded instead, built on 'If he were to', the pattern for unlikely present or future events.

That form occurs in formal English but is not the standard past form. The key marks (1) for departing from 'Had he responded' → option (a).

Why the others are wrong

• (b)
  (2) — 'The crisis could have been' opens a past modal passive, 'could have been averted', which correctly matches a condition about the past. It runs on into segment (3).
• (c)
  (3) — 'Averted far earlier than it ultimately was' is sound. The final was stands for 'was averted', a normal ellipsis after than, and 'far earlier' is a correctly intensified comparative.
• (d)
  (4) — 'Saving valuable diplomatic capital' is an -ing clause of result: averting the crisis early would have saved that capital. It attaches correctly to the clause before it.

Conditionals can drop 'if' by moving the auxiliary before the subject. Each type has its own inverted form:

'If he had responded' → Had he responded (past, did not happen)
'If he were to respond' → Were he to respond (unlikely present or future)
'If he should respond' → Should he respond (possible future)

The main clause tells you which one you need. 'Could have been averted' is past, so the standard choice is the Had form.

Key facts

• Past unreal condition: Had + subject + past participle, then would/could/might have + past participle.
• 'Were + subject + to + verb' inverts 'If + subject + were to + verb' and imagines an unlikely present or future event: 'Were he to resign, the party would split.'
• 'Should + subject + verb' inverts 'If + subject + should + verb': 'Should you need help, call me.'

Common traps

• Marking segment (2) because 'could have been' looks unfinished, when it runs on into 'averted' in segment (3)
• Accepting 'Were he to have responded' because inversion itself is correct, without comparing it with the standard past form, 'Had he responded'

No directly related past PYQ was found.